1. Technical Field
The present invention relates to a cellular mobile communications system comprising a macro-cellular communications network and a plurality of smaller, small-scale cells, for example, femtocells or picocells.
2. Related Art
Macro-scale cellular mobile communications networks are well known in the art. Such communications networks rely on coverage from a macro (exterior) cell tower. However, an exterior signal source for the macro-cellular network does not always provide consistent good network coverage within indoor environments or high user density environments. For example, indoor environments such as large buildings, particularly if these are several floors high, and/or high-user density environments indoors or outdoors where there are a large number of users who require network support within a small geographic region may experience unsuitable signal conditions in contrast to the conditions experienced elsewhere in the network which use a similar network infrastructure. Increasingly however, mobile communications users use their mobile regardless of their location being indoors.
As buildings are often constructed from materials which reduce the signals emitted from exterior cell towers such as concrete etc, even where the coverage from the macro cell penetrates the building a consistent signal strength is unlikely to be supported and there may be areas in the building where little or no mobile network coverage is provided.
Picocell and femtocell cellular communications systems attempt to provide small-scale cells which enhance the network coverage of the macro-cellular network in such environments. This enables a mobile communications network subscriber to use their mobile phone as a primary communications device both within the external (macro-scale) communications network as well as within the internal (small-scale) communications network.
Typically a femtocell may provide a cell which extends to cover a small building, for example, a residential building, whereas a picocell may support a cell coverage area of up to around 30,000 sq feet.
There are several deployment issues which various proposed infrastructures for picocell and femtocell communications systems address. For example, one propose infrastructure uses a distributed antenna system to extend the coverage of a single pico/femtocell. However, this may generate interference with the macro-cell and may not establish a dominant signal source within the building. In contrast, whilst deployment of multiple pico/femtocells can ensure good coverage, interference between cells may result in lower data rates being supported.
In solutions where multiple pico/femto cells are supported, network integration and signalling issues must be addressed. For example, a conventional cellular network is designed to support several thousand or tens of thousands of base stations and is unlikely to be scalable to support a femto-cell deployment of millions of access points.
Ho et al in “Effects of User-deployed, co-channel femtocells on the call drop probability in a residential scenario” published in The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC '07), 1-4244-1144-0/07 IEEE, the contents of which are hereby incorporated by reference, addresses briefly the increased network signalling associated with mobility procedures in the core network. For example, they estimate that handovers per hour could be 12,600 for 1 femtocell user per hour per km2 of coverage if a dynamic power configuration approach is adopted and that alternative solutions to lower the number of femtocell configuration events are to block mobility between femtocells and the underlay macrocell or introduce changes to the network architecture such that the impact of signalling to the core network is more localised, for example, by using a flatter, collapsed cellular architecture.
Other issues include the requirement for an operator to be able to locate each base-station and how to regulate this, for example, for E911 requirements the registered location of a base-station is required.
Scheinert et al in WO2004/040938 and US2005/148368 describe an addressing scheme in which all “mini-cells” are assigned a single identifier associated with an access network controller in a main network. However, in this prior art if a mobile device moves outside the range of the minicells of a controller, a number of issues arise.
In US 2005/148368 one issue occurs when an mobile switching centre MSC receives a mobile terminating call (MTC) for a particular mobile station as the MSC sends a paging command to all base station controllers (iBSCs) that control base stations (BSs) associated with the current location area where the mobile station (MS) last performed an update procedure. In another embodiment, each iBSC has its own visitor location registration functionality. This means that the iBSC sends location information only to the BS where a MS is currently located. If a MS changes its iBS cell, the iBSC is notified of its changed location to the new iBS cell. If, however, the MS moves outside the iBSC network coverage area, no update is performed which US'358 addresses by i) the iBSCs VLR polling MSs regularly in order to determine whether they are still in an iBS cell area of that iBSC or not; ii) by maintaining the MS location information in the iBSC's VLR until the next MTC for that MS arrives and using a two-tier paging procedure; or iii) for the iBSC to page first the “home” cell of the mobile as a default.
It is desirable to minimising the amount of signalling that occurs in communication networks. A compromise is usually made between signalling each location change and the signalling that must occur when a MTC is received for a mobile whose change of location has not been updated. Some embodiments of the present invention seek to address the problem of a macro-cellular network managing call routing and/or other signalling events associated with a small-scale cellular network, particularly but not exclusively by providing a unified addressing scheme for both macrocell and smaller cell location registers. The addressing scheme is associated with a signalling/routing scheme which seeks to route MTCs more efficiently to MSs which may roam between both networks by ensuring the location changes are reported in a more effective manner within the area of overlap between smaller cells which overlay one or more macrocells.
3. Brief Summary
Aspects of the invention are as set out below and in the accompanying independent claims and the embodiments of the invention are as set out below and in the accompanying dependent claims. Those of ordinary skill in the art will find apparent that aspects and embodiments of the invention may be suitably combined with each other in any appropriate manner known to one of ordinary skill in the art.
A first aspect of the invention seeks to provide a cellular communications network system comprising a plurality of wireless network communications base stations of a first type; a plurality of wireless network communications base stations of a second type; a plurality of wireless communication cells of a first type which are provided by said base stations of said first type, each cell providing wireless communications cover over a predetermined geographic region to collectively form a macro-cellular communications network; a plurality of wireless communication cells of a second type which are provided by said base stations of said second type, wherein a plurality of said second type of cells collectively provides wireless communications cover within a region smaller than the predetermined geographic region of said first type of wireless communication cells; a gateway node providing an interface between a routing domain associated with cells of said first type and a routing domain associated with cells of said second type; a routing node for routing communications and signalling in said macro-cellular communications network; and a first location register for registering the location of a plurality of mobile communications devices in one or more cells of said first type in said macro-cellular communications network; wherein the first location register records the location of at least one of said mobile communications device as a virtual location if the said mobile communication device reports its location to a routing node for said macro-cellular communications network as within one of a predetermined plurality of wireless communication cells of said second type.
The first location register may record the location of the said mobile communications device as said virtual location instead of recording the location of the device in a cell of said first type.
Alternatively, the first location register may record the location of the said mobile communications device as said virtual location in addition to recording the location of the device in a cell of said first type.
The location of the said mobile communications device is provided as a cell identifier in said location registry.
The identifier for the cell of the second type may be provided to said first location register in addition to the virtual cell identifier by said mobile communications device.
The virtual cell identifier for the cell of the second type may be stored on said first location register instead of the identifier for the cell of the first type.
Another aspect of the invention seeks to provide a method of routing call signalling to a destination address, said method routing the call signalling from a first cellular mobile communications network comprising a plurality of cells to one of a plurality of smaller cells collectively identified in said first mobile communications network by a single virtual cell identifier, the method comprising: receiving call signalling for a call in a first routing domain associated with said first mobile communications network; determining in said first routing domain from said destination address a forwarding address for said call signalling, wherein said forwarding address comprises said virtual cell identifier; forwarding said call signalling to a network gateway node associated with said virtual cell identifier in said first routing domain, said gateway node being further arranged to participate in a different routing domain by identifying, using said different routing domain, the identity of one of said smaller cells associated with said destination address; and routing the call signalling to said destination address.
The first routing domain may be associated with a first location register for identifying a cell location of a called mobile communications device, wherein the location of said mobile communications device is identified as being in said virtual cell in said first cellular mobile communications device.
The different routing domain may be associated with another location register, wherein said mobile communications device is identified as being in one of said smaller cells in said other location register.
In said first location register the virtual cell identifier and the cell identifier of said smaller cell in which said mobile communications device is located may be stored and in said first routing domain only said virtual cell identifier may be used for routing purposes. The method aspect may further comprise modifying said call signalling in said macro-cellular network to provide an indication of the identity of said smaller destination cell in which said mobile communications device is located to said gateway node, whereby said gateway node forwards said call signalling to the base station associated with the smaller destination cell.
The plurality of smaller cells collectively identified in said first mobile communications network by a single virtual cell identifier may form a second cellular communications network.
The gateway node may comprise a wireless access point for one of said plurality of smaller cells collectively identified by said virtual cell identifier.
One or more of said smaller cells may comprise a femtocell. One of said smaller cells may comprise a picocell.
Another aspect of the invention relates to a method of registering a mobile communications device in a communications system comprising a first cellular communications network and at least one second cellular mobile communications network comprising a plurality of cells of smaller size than the cells in said first cellular communications network, wherein said mobile communications device is capable of receiving calls sent using the first communications network using the network infrastructure of the second communications network, the method comprising:                registering a virtual cell location of a mobile communications device in a first location register for said communications system, said virtual cell location collectively representing the cell identity of the plurality of cells which collectively form said second cellular network; and        registering a cell location for the location of the mobile device in said second cellular network in a second location register accessible within said second cellular network,        wherein both location register entries are required to route calls originating external to said second cellular network to said destination location in said second cellular network by firstly determining the virtual cell location of the called mobile communications device in the first location register and secondly determining the cell location of said called mobile communications device in said second cellular network in a second location register.        
One or more cells in said second location register may comprise a femtocell.
One or more cells in said second location register may comprise a picocell.
Another aspect of the invention relates to a communications system comprising a macro-cellular mobile communications network and a plurality of smaller, cells collectively identified in said macro-cellular network by implementing a registration scheme according a method of registering aspect of the invention.
Another aspect of the invention seeks to provide a communications system aspect in which the macro-cellular mobile communications network comprises a radio access network comprises one of the following types of mobile communications networks:
a Global System for Mobile (GSM) network; a Worldwide Interoperability for Microwave Access (Wi-MAX) network; a General Packet Radio Service (GPRS) network; a Generation Partnership Project (3GPP) network; or any other suitable 4th or higher generation radio access network.
GSM is the standard for digital cellular communications that has been widely adopted across Europe and other territories. The GSM standard operates in the 900 MHz and 1800 MHz bands and provides a host of services using a sophisticated signalling system.
WI-MAX is a standards based technology known as IEEE 802.16 which is able to provide fixed and mobile broadband access at large coverage distances in Line of Sight and Non Line of Sight conditions. The technology provides high-throughput broadband connections, enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL.
GPRS is a standardised dedicated data service based on a separate packet data network which allows up to 8 GSM channels to be concatenated together giving a possible bit rate of over 70 kbits/s. GPRS basically provides a connectionless service for GSM. It uses IP as the backbone for transmission introducing a new network to support the connectionless nature but shares the base station and radio resource.
A 3GPP network is a network for which the 3GPP has produced a globally applicable technical specifications and technical report. Typically, a 3GPP network comprises a 3rd Generation mobile communications system based on an evolved GSM core network and a supported radio access technology such as, for example, Universal Terrestrial Radio Access (UTRA) in a Frequency Division Duplex (FDD) and/or Time Division Duplex (TDD) mode. In addition, a 3GPP network is specified to include the maintenance and development of the Global System for Mobile communication (GSM) Technical Specifications and Technical Reports including evolved radio access technologies (e.g. General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE)).
Another aspect of the invention seeks to provide a base station for use as a gateway node in a communications system aspect, the base station being associated in the macro-cellular communications network with said virtual cell identifier and arranged to resolve the signalling addressed to said virtual cell identifier to an identifier for a cell in said second communications network associated in said second location register with the cell location of the destination device for the incoming call.
Another aspect of the invention seeks to provide a method of routing signalling for a call in a cellular communications network system, the system comprising: a first wireless communications network having: a mobile switching centre; a plurality of macro-cell base stations, each said macro-cell base station being associated with a macrocell of network cover; and at least one macrocell location register, wherein the first wireless communications network shares at least some of its area of network coverage with at least one second wireless communications network, wherein said a said at least one second wireless communications network comprises a gateway node for a plurality of small cell base stations providing smaller cellular areas of network coverage than said macro-cells, each small cell base station being arranged to report a change of small cell location address of a mobile device to said gateway node; wherein, said gateway node is configured to forward a received change of small cell location from a said small cell base station to the macrocell location register together with a virtual macrocell identifier, the virtual macrocell identifier identifying a gateway node for a plurality of associated small cells; the method comprising: said mobile switching centre receiving said mobile terminating call for a mobile device; said macrocell location register indicating to the mobile switching centre that the mobile is located in said virtual location cell; forwarding the call signalling to the gateway node associated with said virtual location cell, said signalling including the small cell location of the mobile device; the gateway node processing the received call signalling information to extract the small cell location; and forwarding the call signalling to the base station associated with the indicated small cell location.
Another aspect of the invention seeks to provide a cellular communications network system, the system comprising: a first wireless communications network having:                a mobile switching centre; a plurality of macro-cell base stations, each said macro-cell base station being associated with a macrocell of network cover; and at least one macrocell location register, wherein the first wireless communications network shares at least some of its area of network coverage with at least one second wireless communications network, wherein said a said at least one second wireless communications network comprises: a gateway node for a plurality of small cell base stations providing smaller cellular areas of network coverage than said macro-cells, each small cell base station being arranged to report a change of small cell location address of a mobile device to said gateway node; wherein, said gateway node is configured to forward a received change of small cell location from a said small cell base station to the macrocell location register together with a virtual macrocell identifier, the virtual macrocell identifier identifying the gateway node as being the gateway for said plurality of associated small cells; and said macrocellular location register stores a location address for a mobile device as comprising said virtual macrocell identifier and said small cell location identifier.        
In this way, the macrocell location register can store a full location address comprising a virtual cell location which indicates that a call should be forwarded to a gateway node which provides access to a plurality of small cells. To reduce the signalling the gateway node provides, the small cell address location can also be stored in the macrocell location register, but this part of the location address is not used for routing in the macrocell network. It is only when a gateway node receives signalling associated with a virtual cell that the gateway node processes the provided location address to extract the location of the small cell. This means that instead of having to poll a plurality of different cells, the gateway node will simply forward the signalling to the base station indicated in the macrocell location register. This implementation assumes that the gateway node will also have forwarded changes to the small cell location to the macrocell location register as well as to its own location register. If a mobile device (or equivalently station) then moves outside the range of a particular gateway, the macrocell entry will be updated to replace the virtual cell with the new macrocell identifier (which may be a virtual or “normal” macrocell identifier). This means that when a mobile moves outside the virtual cell coverage area, the call signalling (and so the call itself) will not be forwarded to the gateway associated with that particular virtual cell, triggering a needless poll of base stations within the area of that virtual cell identifier. In one embodiment, the gateway node may also update a location register for the small area cells so that if a change occurs which for some reason has not yet propagated to the macrocell network, this can be corrected at the gateway node.
If a small cell location register may be associated with the gateway node and used to store the location of a mobile device in association with the small cell base station within whose area of network coverage the mobile device is located, the gateway node is required to ensure both the macro and small cell location registers are updated with any location changes.